This invention relates to a device manufacturing method usable for the manufacture of various electronic devices such as semiconductor chips (e.g., ICs or LSIs), display devices (e.g., magnetic heads) or image pickup devices (e.g., CCDs), for example.
The density and speed of a semiconductor integrated circuit have been increased more and more, and the linewidth of an integrated circuit pattern has been narrowed more and more. This requires further improvements in semiconductor manufacturing methods. In some exposure apparatuses to be used for resist pattern formation in a lithographic process, among various semiconductor manufacturing processes, very short wavelengths of X-rays or extreme ultraviolet rays such as a KrF laser (248 nm), an ArF laser (193 nm), or an F2 laser (157 nm) are used.
In an exposure process using extreme ultraviolet rays, mainly a reduction exposure of xc2xc-⅕ is performed. A mask or reticle (original) is therefore formed with a pattern of a size magnified by 4xc3x97 or 5xc3x97 as compared with a pattern to be produced on a semiconductor wafer (substrate to be exposed). In a unit-magnification X-ray proximity exposure process, on the other hand, an X-ray mask (original) is formed with a pattern of the same size as a pattern to be produced on a substrate.
Conventionally, one mask is used for exposure of a single layer upon a substrate. With this method, however, even if the exposure wavelength is shortened, there occurs an error (to be described later) which could not be disregarded in connection with the resolution and positional precision required, and it creates a limitation to the resolution and positional precisiion.
First, as regards an electron beam patterning apparatus which is used in the manufacture of originals, since the electron beam irradiation position is controlled by applying an electromagnetic field or electrostatic field to an electron beam to cause deflection thereof, the controllability of an electric voltage to be applied to a deflector is influential to the pattern position control. Further, depending on the flatness (irregularity) of a workpiece to be patterned, a pattern position distortion occurs.
In an exposure process using extreme ultraviolet rays, since the exposure process is performed by use of an original having been manufactured by use of an electron beam patterning apparatus such as described above, in addition to the positional distortion of the original itself, there occurs a pattern position distortion on a wafer due to aberrations produced in a projection optical system.
In an X-ray proximity exposure process, in addition to the positional distortion of an original itself produced by an electron beam patterning apparatus, there occurs a distortion of an X-ray mask. That is, usually, in an X-ray mask, a pattern of an X-ray absorptive material having a thickness of about 0.4 micron is formed on an X-ray transmissive film having a thickness of about 2 microns, for example. Due to a stress distribution of the transmissive film or to a stress of the absorptive material, a positional distortion occurs. Further, during the X-ray proximity exposure process, since the X-ray beam is not a completely parallel beam, there occurs a distortion, called a runout error.
Japanese Published patent Application No. 11-143085, filed by the same assignee of the subject application, proposes an exposure method which assures pattern formation of a higher resolution and a higher positional precision, as compared with those attainable currently, by use of a mask that can be produced by current techniques and an exposure apparatus currently available. In this exposure method, a fine pattern exposure and a rough pattern exposure are performed superposedly (by dual or multiple exposure) upon a layer on a substrate, to thereby assure enhancement of resolution. This method will be briefly explained below.
The fine pattern exposure is an exposure process for a pattern having a periodic structure. To a layer on a substrate having a fine pattern photoprinted thereon, a rough pattern having a desired pattern corresponding to those portions to be left is printed by dual or multiple exposures. Then, a development process is performed thereto, under a condition by which the fine pattern at those portions (positions) having been exposed to the rough pattern remain. The fine pattern exposure amount and the rough pattern exposure amount are determined at a ratio by which a best resist pattern is obtainable.
In accordance with such a dual or multiple exposure method described above, as compared with a conventional exposure method wherein one original is used for exposure of a single layer on a substrate, the influence attributable to the problems described hereinbefore can be reduced and, therefore, the resolution and positional precision can be improved.
It is an object of the present invention to provide a device manufacturing method by which a pattern registration precision between layers on a substrate in a multiple exposure process (including a dual exposure process) can be increased, such that a pattern can be produced with higher resolution and precision.
In accordance with an aspect of the present invention, there is provided a device manufacturing method including a process for exposure of a first layer on a substrate and a process for exposure of a second layer on the substrate, wherein each exposure of the first and second layers is performed by use of a plurality of originals, and wherein at least one of the originals to be used for exposure of the first layer has the same design rule as that of at least one of the originals to be used for exposure of the second layer.
The masks having the same design rule may be an identical mask to be used for exposures of both the first and second layers.
At least a portion of the first or second layer may be exposed by use of at least one of an X-ray, an ultraviolet ray, an extreme ultraviolet ray, and an electron beam.
Each of the first and second layers may be exposed superposedly by use of a fine pattern original having a relatively fine pattern and a rough pattern original having a relatively rough pattern.
Each fine pattern to be printed on the first and second layers may have a periodic structure. Each rough pattern to be printed on the first and second layers may comprise different patterns.
In the present invention, for dual or multiple exposures of different layers on a substrate, at least one pattern for each layer includes a portion having a common design rule. As a result of it, the pattern registration precision between different layers can be improved significantly. Thus, with the present invention, a pattern can be produced at higher resolution and precision, with a good registration precision between different layers.
As regards plural originals (masks or reticles) to be used in the present invention, at least two originals may be used, including, for example, a first original for printing a fine pattern having a relatively small minimum linewidth upon a layer on a substrate and a second original for printing a rough pattern, formed with a target precision corresponding to a minimum linewidth larger than that of the fine pattern.
The term xe2x80x9cfirst layerxe2x80x9d referred to in this specification is not limited to a layer first provided on a bare wafer. It may include an initial layer of two or more layers to be provided superposedly. The term xe2x80x9csecond layerxe2x80x9d refers to a layer which is superposedly provided after formation of a xe2x80x9cfirst layerxe2x80x9d. Further, it is not always necessary that a xe2x80x9cfirst layerxe2x80x9d and a xe2x80x9csecond layerxe2x80x9d are formed successively. Namely, after a certain layer is formed subsequent to formation of a xe2x80x9cfirst layerxe2x80x9d, a xe2x80x9csecond layerxe2x80x9d may be formed superposedly on the xe2x80x9cfirst layerxe2x80x9d.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.